Published Aug 24, 2018 at 7:09 AM

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This file photo shows a sign at the northeast entrance into Yellowstone National Park in Wyoming.

A bear charged a family hiking in Yellowstone National Park on Thursday, knocking down and injuring a 10-year-old boy before his parents were able to drive the animal off with bear spray, park officials said.

The unidentified boy from Washington state was transferred to a hospital for puncture wounds to his back, wounds around his buttocks and an injured wrist, park officials said in a statement. It's unclear how serious his injuries are, spokeswoman Morgan Warthin said.

The park is home to grizzly and black bears, both of which are a top draw for the more than 4 million tourists who visit each year. It's not clear whether the bear that attacked the boy was a grizzly or a black bear.

Yellowstone averages about one bear attack on a human per year, but it's been three years since the last attack within in park boundaries, according to officials.

The family of four was hiking along the Divide Trail southeast of Old Faithful when the bear charged from the vegetation, chased the boy and knocked him to the ground, park officials said in the statement.

It wasn't immediately clear what caused the bear to charge.

The boy's parents deployed bear spray about 5 feet (1 ½ meters) from the bear's head, causing it to leave. The family walked to the trailhead and drove to the ranger station at Old Faithful, where they were sent to a nearby clinic.